1. Field of the Invention
The present invention relates to a laminated sheet usable in the manufacture of a semiconductor device, a method for manufacturing a semiconductor device using the sheet, and a semiconductor device which can be manufactured by the method.
2. Discussion of the Related Art
As the recent requirements accompanied by multi-functionality and miniaturization of a semiconductor device, a flip-chip mounting in which a semiconductor element is mounted on a wiring circuit board with a facedown structure has been carried out.
Generally, in the flip-chip mounting, resin encapsulation is carried out at a gap between a semiconductor element and a wiring circuit board in order to protect the semiconductor element. A conventional manufacturing method with flip-chip mounting comprises the step of creating patterns on a wafer, forming bumps, grinding the wafer to a given thickness, cutting the wafer into individual semiconductor elements, and mounting the semiconductor elements on a wiring circuit board and carrying out resin encapsulation.
There has been a defect that a thin wafer subjected to grinding has a low mechanical strength against an external force. As a measure for its improvement, there has been proposed to make up for the deficiency in mechanical strength of the wafer after grinding by previously resin-encapsulating a projection electrode-mounting wafer, and thereafter carrying out a backside grinding of the wafer (for instance, Japanese Patent Laid-Open No. 2001-144123). However, in order to form electrodes for mounting a semiconductor device on a wiring circuit board, there arises a problem that complicated steps of opening holes corresponding to the positions of the electrodes of the wafer in the resin-encapsulating layer, embedding solders to the open holes, and thereafter forming solder balls in the holes are necessitated.
In addition, there has been proposed a method comprising the steps of forming an adhesive film layer so as to completely cover the electrodes on the projection electrode-mounting wafer, subjecting the wafer to a backside grinding using the adhesive film as a projection electrode-protective layer, thereafter dividing the wafer into individual chips, and mounting on a circuit board (for instance, Japanese Patent Laid-Open No. 2001-144140). In this case, since the adhesive film layer completely covers the projection electrodes, the adhesive film layer which is an insulation is mechanically pushed away in an electric connection with the circuit board, so that electric connection must be secured, thereby causing a problem in connection reliability. Also, since the adhesive film layer completely covers the projection electrodes, a resin is applied in an amount exceeding that required for filling the gap between the semiconductor elements and the circuit board, so that an excess resin is pressed out in a wide range in the surroundings of the semiconductor elements after mounting the chips, thereby causing some problems in high-density mounting.
On the other hand, there has been proposed a method comprising coating a thermoplastic resin in an amount that exposes the top of the electrode of the projection electrode side of the wafer, thereafter adhering a tape with an adhesive layer to the thermoplastic resin and subjecting the wafer to a backside grinding (for instance, Japanese Patent Laid-Open No. 2000-223602). In the proposed method, after the backside grinding, the tape with an adhesive layer is stripped off, the wafer is divided into individual chips, and thereafter the chips are mounted on the circuit board with melting the thermoplastic resin. In this method, sufficient activity is necessary for uniformly applying the thermoplastic resin. Since a preferred embodiment proposes to drop a thermoplastic resin which plasticizes at about 150° C., while heating to 240° to 260° C., there arises a problem of failure in transporting the wafer by generation of bowing accompanied by the residual stress of the thermoplastic resin in the wafer after grinding.